Telescoping booms are employed in machines as varied as cranes, excavators, concrete pumps, elevated work platforms and drill rigs.
A typical telescopic boom assembly comprises telescoping boxlike boom sections and several adjustable wear buttons working against each sliding surface of the boom sections to smoothly guide the moving boom sections through extension and retraction. The wear buttons are adjustable to compensate for wear thereof, which would otherwise permit free play, or slop between the boom sections.
A typical wear button comprises steel backing and adjuster parts for a bronze wear button. The steel backing piece comprises a male thread which screws into a female thread of the steel adjuster housing part of the boom, so that the wear button can be adjusted. There is generally a locking cover which is also screwed into the adjuster housing female thread to lock against the steel adjuster and prevent movement.
In typical applications the adjuster is required to handle up to 100 tons of load, and can be subject to repetitive shock load. The adjusters and locking plates of previous wear buttons work loose after a short period of service, so they then can unwind and/or begin to wear both the adjuster's male thread, and the boom's female thread, making the adjuster inherently subject to jamming, cross threading, or the adjuster being ejected from the boom. A partially ejected or cross threaded adjuster is extremely difficult to remove once failed.
It is against this background and the problems and difficulties associated therewith that the present invention has been developed.
Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.